Effect of High Temperature and Dietary Fat on Milk Fatty Acids

Abstract Two Latin squares balanced for carry on effects were used to study milk fat composition C 12:0 to C 18:2 of 12 cows fed high fat under environmental temperatures: cool 15 to 24C and a constant hot 32.2C with 60% relative humidity. Cows were fed daily: alfalfa-grass hay at 1.25% their body weight and one of three concentrates: control (without added lipids), oil (10% soybean oil), or fat (10% hydrogenated vegetable fat, iodine value 48) replacing corn by weight. The 32.2C temperature depressed proportion of milk fatty acids C 12:0 , C 14:1 to 15:0 , C 18:1 and C 18:2 while increasing C 16:0 and C 18:0 . Both dietary oil and fat depressed concentrations of C 12:0 , C 14:0 , C 14:1 to 15:O , C 15:1 , and C 16:0 but increased C 18:0 and C 18:1 . Compared with fat, dietary oil depressed C 16:0 more while increasing C 18:2 . Thermal stress increased C 18:0 more when the cows were receiving oil than fat. Cow differences were observed only with C 18:l , and proportions of C 18:0 increased and C 18:1 decreased with repeated exposure to heat.